3 perldelta - what is new for perl v5.9.5
7 This document describes differences between the 5.9.4 and the 5.9.5
8 development releases. See L<perl590delta>, L<perl591delta>,
9 L<perl592delta>, L<perl593delta> and L<perl594delta> for the differences
10 between 5.8.0 and 5.9.4.
12 =head1 Incompatible Changes
14 =head2 Tainting and printf
16 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
17 reject any tainted format argument. (Rafael Garcia-Suarez)
19 =head2 undef and signal handlers
21 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
22 equivalent to setting it to C<'DEFAULT'>.
24 =head2 Removal of the bytecode compiler and of perlcc
26 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
27 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
28 experimental tools have never worked reliably, and, due to the lack of
29 volunteers to keep them in line with the perl interpreter developments, it
30 was decided to remove them instead of shipping a broken version of those.
31 The last version of those modules can be found with perl 5.9.4.
33 However the B compiler framework stays supported in the perl core, as with
34 the more useful modules it has permitted (among others, B::Deparse and
37 =head2 Removal of the JPL
39 The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
41 =head1 Core Enhancements
43 =head2 Regular expressions
47 =item Recursive Patterns
49 It is now possible to write recursive patterns without using the C<(??{})>
50 construct. This new way is more efficient, and in many cases easier to
53 Each capturing parenthesis can now be treated as an independent pattern
54 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
55 "parenthesis number"). For example, the following pattern will match
56 nested balanced angle brackets:
60 ( # start capture buffer 1
61 < # match an opening angle bracket
63 (?> # don't backtrack over the inside of this group
64 [^<>]+ # one or more non angle brackets
65 ) # end non backtracking group
67 (?1) # recurse to bracket 1 and try it again
69 > # match a closing angle bracket
70 ) # end capture buffer one
74 Note, users experienced with PCRE will find that the Perl implementation
75 of this feature differs from the PCRE one in that it is possible to
76 backtrack into a recursed pattern, whereas in PCRE the recursion is
77 atomic or "possessive" in nature. (Yves Orton)
79 =item Named Capture Buffers
81 It is now possible to name capturing parenthesis in a pattern and refer to
82 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
83 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
84 syntax. In code, the new magical hash C<%+> can be used to access the
85 contents of the buffers.
87 Thus, to replace all doubled chars, one could write
89 s/(?<letter>.)\k<letter>/$+{letter}/g
91 Only buffers with defined contents will be "visible" in the hash, so
92 it's possible to do something like
94 foreach my $name (keys %+) {
95 print "content of buffer '$name' is $+{$name}\n";
98 Users exposed to the .NET regex engine will find that the perl
99 implementation differs in that the numerical ordering of the buffers
100 is sequential, and not "unnamed first, then named". Thus in the pattern
102 /(A)(?<B>B)(C)(?<D>D)/
104 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
105 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
106 would expect. This is considered a feature. :-) (Yves Orton)
108 =item Possessive Quantifiers
110 Perl now supports the "possessive quantifier" syntax of the "atomic match"
111 pattern. Basically a possessive quantifier matches as much as it can and never
112 gives any back. Thus it can be used to control backtracking. The syntax is
113 similar to non-greedy matching, except instead of using a '?' as the modifier
114 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
115 quantifiers. (Yves Orton)
117 =item Backtracking control verbs
119 The regex engine now supports a number of special-purpose backtrack
120 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
121 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
123 =item Relative backreferences
125 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
126 safer form of back-reference notation as well as allowing relative
127 backreferences. This should make it easier to generate and embed patterns
128 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
130 =item Regexp::Keep internalized
132 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
133 the core. You can now use in regular expressions the special escape C<\K>
134 as a way to do something like floating length positive lookbehind. It is
135 also useful in substitutions like:
139 that can now be converted to
143 which is much more efficient.
147 =head2 The C<_> prototype
149 A new prototype character has been added. C<_> is equivalent to C<$> (it
150 denotes a scalar), but defaults to C<$_> if the corresponding argument
151 isn't supplied. Due to the optional nature of the argument, you can only
152 use it at the end of a prototype, or before a semicolon.
154 This has a small incompatible consequence: the prototype() function has
155 been adjusted to return C<_> for some built-ins in appropriate cases (for
156 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
158 =head2 UNITCHECK blocks
160 C<UNITCHECK>, a new special code block has been introduced, in addition to
161 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
163 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
164 are always executed at the transition between the compilation and the
165 execution of the main program, and thus are useless whenever code is
166 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
167 just after the unit which defined them has been compiled. See L<perlmod>
168 for more information. (Alex Gough)
170 =head2 readpipe() is now overridable
172 The built-in function readpipe() is now overridable. Overriding it permits
173 also to override its operator counterpart, C<qx//> (a.k.a. C<``>). (Rafael
178 The copy of the Unicode Character Database included in Perl 5.9 has
179 been updated to version 5.0.0.
181 =head1 Modules and Pragmas
183 =head2 New Core Modules
189 C<Locale::Maketext::Simple>, needed by CPANPLUS, is a simple wrapper around
190 C<Locale::Maketext::Lexicon>. Note that C<Locale::Maketext::Lexicon> isn't
191 included in the perl core; the behaviour of C<Locale::Maketext::Simple>
192 gracefully degrades when the later isn't present.
196 C<Params::Check> implements a generic input parsing/checking mechanism. It
201 C<Term::UI> simplifies the task to ask questions at a terminal prompt.
205 C<Object::Accessor> provides an interface to create per-object accessors.
209 =head2 Module changes
215 The C<base> pragma now warns if a class tries to inherit from itself.
219 The C<warnings> pragma doesn't load C<Carp> anymore. That means that code
220 that used C<Carp> routines without having loaded it at compile time might
221 need to be adjusted; typically, the following (faulty) code won't work
222 anymore, and will require parentheses to be added after the function name:
226 Carp::confess "argh";
228 =item C<Attribute::Handlers>
230 C<Attribute::Handlers> can now report the caller's file and line number.
235 =head1 Utility Changes
239 =head1 Performance Enhancements
241 =head1 Installation and Configuration Improvements
243 =head2 C++ compatibility
245 Efforts have been made to make perl and the core XS modules compilable
246 with various C++ compilers (although the situation is not perfect with
247 some of the compilers on some of the platforms tested.)
249 =head2 Static build on Win32
251 It's now possible to build a C<perl-static.exe> that doesn't depend
252 on C<perl59.dll> on Win32. See the Win32 makefiles for details.
257 Perl has been reported to work on MidnightBSD.
259 =head1 Selected Bug Fixes
261 PerlIO::scalar will now prevent writing to read-only scalars. Moreover,
262 seek() is now supported with PerlIO::scalar-based filehandles, the
263 underlying string being zero-filled as needed.
265 study() never worked for UTF-8 strings, but could lead to false results.
266 It's now a no-op on UTF-8 data. (Yves Orton)
268 The signals SIGILL, SIGBUS and SIGSEGV are now always delivered in an
269 "unsafe" manner (contrary to other signals, that are deferred until the
270 perl interpreter reaches a reasonably stable state; see
271 L<perlipc/"Deferred Signals (Safe Signals)">).
273 When a module or a file is loaded through an @INC-hook, and when this hook
274 has set a filename entry in %INC, __FILE__ is now set for this module
275 accordingly to the contents of that %INC entry.
277 =head1 New or Changed Diagnostics
279 =head1 Changed Internals
281 The anonymous hash and array constructors now take 1 op in the optree
282 instead of 3, now that pp_anonhash and pp_anonlist return a reference to
283 an hash/array when the op is flagged with OPf_SPECIAL (Nicholas Clark).
285 =head1 Known Problems
287 =head2 Platform Specific Problems
289 =head1 Reporting Bugs
291 If you find what you think is a bug, you might check the articles
292 recently posted to the comp.lang.perl.misc newsgroup and the perl
293 bug database at http://rt.perl.org/rt3/ . There may also be
294 information at http://www.perl.org/ , the Perl Home Page.
296 If you believe you have an unreported bug, please run the B<perlbug>
297 program included with your release. Be sure to trim your bug down
298 to a tiny but sufficient test case. Your bug report, along with the
299 output of C<perl -V>, will be sent off to perlbug@perl.org to be
300 analysed by the Perl porting team.
304 The F<Changes> file for exhaustive details on what changed.
306 The F<INSTALL> file for how to build Perl.
308 The F<README> file for general stuff.
310 The F<Artistic> and F<Copying> files for copyright information.